A method for operating a coolant circuit of an internal combustion engine, in which the coolant circuit is comprised of at least one main coolant pump, at least one block cooling circuit and at least one EGR cooler, in which the EGR cooler is connected to a heat exchanger circuit is described herein.
Separate or predominantly separate flows of a coolant through the engine block and the cylinder head of an internal combustion engine are known. As a result of having separate flows, the cylinder head, which is thermally coupled to a combustion chamber wall, the intake air duct and the exhaust duct, and the engine block, which is thermally coupled especially to friction points, can be cooled differently. This “split cooling system”, wherein separate cooling circuits are included that allow differential control of the coolant flow through each part independently, ensures that the cylinder head can be cooled during the warm-up phase of the internal combustion engine, while coolant flow through the engine block is blocked, thus allowing the temperature of the engine block to be brought up to operating temperature more quickly. Herein, the term “separate cooling circuits” refers to a cooling circuit for an internal combustion engine in which the water jacket of the cylinder head is separated from the water jacket of the cylinder block by suitable means. It is not intended as an indication of two cooling circuits. However, in many designs, the cylinder head water jacket and cylinder block water jacket may be coupled so minor leaks from the cylinder head water jacket to the cylinder block water jacket can also occur. In these systems, because the leakage volumes are small, it is nevertheless possible to speak of a separate cooling circuit.
A procedure for shortening the warm-up phase of engines is known wherein the flow of coolant in the block cooling circuit is blocked, which results in no circulation of coolant through the system. A blocked cooling circuit is also referred to as the “no flow status”. This procedure allows the operating media for an internal combustion engine, e.g. the engine oil, to be heated up more quickly and leads to advantages in terms of reduced fuel consumption. However, block coolant circuits may also contain an Exhaust Gas Recirculation (EGR) cooler integrated into the coolant circuit in order to cool recirculated exhaust gases. Thus, in some embodiments, the recirculated exhaust gases may be cooled when the block coolant circuit operates in a no flow status, which makes it necessary to abandon the no flow status and thereby unblock the coolant flow in order to circulate coolant through the system even though the warm-up phase of the engine has not yet ended. When the no flow status is abandoned, advantages with regard to fuel savings, for example, by heating the engine oil in the manner described above may be lost.
To counter this, systems are known that include example cooling systems with an EGR cooler integrated into a separate EGR coolant circuit. For example, in one system shown in FIG. 1, the EGR coolant circuit branches off from the block coolant circuit downstream of a main water pump but upstream of a block coolant inlet. The coolant is then carried to a cab heat exchanger, flowing via the EGR cooler, and, after emerging from said heat exchanger, flows back to the main water pump via a return line. Downstream of the cab heat exchanger and upstream of the main coolant pump, an auxiliary coolant pump is included therein, which allows the no flow status of the block coolant circuit to be maintained, despite the cooling of the recirculated exhaust gases. However, one disadvantage of such systems is the inclusion of additional connecting lines from the main coolant pump to the EGR cooler. Extra equipment leads to higher production costs and also additional weight for the motor vehicle, which further leads to disadvantages in terms of fuel consumption.
Herein the inventors have recognized the abovementioned disadvantages, and have developed a method for operating a coolant circuit of an internal combustion engine in two different modes. The liquid-coolant circuit described herein includes at least one main coolant pump, at least one block cooling circuit and at least one EGR cooler, in which the EGR cooler is connected to a heat exchanger circuit, and wherein recirculated exhaust gases can be cooled, despite the maintenance of a no flow status of the block coolant circuit.
In one embodiment, the EGR cooler is connected to the block cooling circuit or an outlet thereof by a connecting line, wherein the flow of coolant through the system can be adjusted such that the flow through a bypass line during a second operational mode is reversed during the no flow status of the block cooling circuit, and wherein the flow in the second operating mode is brought about by an auxiliary coolant pump. In comparison with known methods, the liquid-cooling circuit disclosed herein reduces production costs and, in particular, reduces weight since it is possible to dispense with additional lines. Further advantages are also possible since the power of the main coolant pump can be reduced since it does not have to operate against the flow resistance of additional lines. It is also possible to make the cooling of the recirculated exhaust gases independent of the load on the internal combustion engine by using an electric main coolant pump, for example, which is not in operative connection with the crankshaft of the internal combustion engine, unlike conventional main coolant pumps.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.